Apply unit conversion early in errorbar().

This allow using normal numpy constructs rather than manually looping
and broadcasting.

_process_unit_info was already special-handling `data is None` in a few
places; the change here only handle the (theoretical) extra case where a
custom unit converter would fail to properly pass None through.

Author: anntzer

lib/matplotlib/axes/_axes.py

@@ -3281,27 +3281,19 @@ def errorbar(self, x, y, yerr=None, xerr=None,
         kwargs = {k: v for k, v in kwargs.items() if v is not None}
         kwargs.setdefault('zorder', 2)
 
-        self._process_unit_info([("x", x), ("y", y)], kwargs, convert=False)
-
-        # Make sure all the args are iterable; use lists not arrays to preserve
-        # units.
-        if not np.iterable(x):
-            x = [x]
-
-        if not np.iterable(y):
-            y = [y]
-
+        # Casting to object arrays preserves units.
+        if not isinstance(x, np.ndarray):
+            x = np.asarray(x, dtype=object)
+        if not isinstance(y, np.ndarray):
+            y = np.asarray(y, dtype=object)
+        if xerr is not None and not isinstance(xerr, np.ndarray):
+            xerr = np.asarray(xerr, dtype=object)
+        if yerr is not None and not isinstance(yerr, np.ndarray):
+            yerr = np.asarray(yerr, dtype=object)
+        x, y = np.atleast_1d(x, y)  # Make sure all the args are iterable.
         if len(x) != len(y):
             raise ValueError("'x' and 'y' must have the same size")
 
-        if xerr is not None:
-            if not np.iterable(xerr):
-                xerr = [xerr] * len(x)
-
-        if yerr is not None:
-            if not np.iterable(yerr):
-                yerr = [yerr] * len(y)
-
         if isinstance(errorevery, Integral):
             errorevery = (0, errorevery)
         if isinstance(errorevery, tuple):
@@ -3313,10 +3305,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
                 raise ValueError(
                     f'errorevery={errorevery!r} is a not a tuple of two '
                     f'integers')
-
         elif isinstance(errorevery, slice):
             pass
-
         elif not isinstance(errorevery, str) and np.iterable(errorevery):
             # fancy indexing
             try:
@@ -3328,6 +3318,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
         else:
             raise ValueError(
                 f"errorevery={errorevery!r} is not a recognized value")
+        everymask = np.zeros(len(x), bool)
+        everymask[errorevery] = True
 
         label = kwargs.pop("label", None)
         kwargs['label'] = '_nolegend_'
@@ -3410,13 +3402,8 @@ def errorbar(self, x, y, yerr=None, xerr=None,
         xlolims = np.broadcast_to(xlolims, len(x)).astype(bool)
         xuplims = np.broadcast_to(xuplims, len(x)).astype(bool)
 
-        everymask = np.zeros(len(x), bool)
-        everymask[errorevery] = True
-
-        def apply_mask(arrays, mask):
-            # Return, for each array in *arrays*, the elements for which *mask*
-            # is True, without using fancy indexing.
-            return [[*itertools.compress(array, mask)] for array in arrays]
+        # Vectorized fancy-indexer.
+        def apply_mask(arrays, mask): return [array[mask] for array in arrays]
 
         def extract_err(name, err, data, lolims, uplims):
             """
@@ -3437,24 +3424,14 @@ def extract_err(name, err, data, lolims, uplims):
                 Error is only applied on **lower** side when this is True.  See
                 the note in the main docstring about this parameter's name.
             """
-            try:  # Asymmetric error: pair of 1D iterables.
-                a, b = err
-                iter(a)
-                iter(b)
-            except (TypeError, ValueError):
-                a = b = err  # Symmetric error: 1D iterable.
-            if np.ndim(a) > 1 or np.ndim(b) > 1:
+            try:
+                low, high = np.broadcast_to(err, (2, len(data)))
+            except ValueError:
                 raise ValueError(
-                    f"{name}err must be a scalar or a 1D or (2, n) array-like")
-            # Using list comprehensions rather than arrays to preserve units.
-            for e in [a, b]:
-                if len(data) != len(e):
-                    raise ValueError(
-                        f"The lengths of the data ({len(data)}) and the "
-                        f"error {len(e)} do not match")
-            low = [v if lo else v - e for v, e, lo in zip(data, a, lolims)]
-            high = [v if up else v + e for v, e, up in zip(data, b, uplims)]
-            return low, high
+                    f"'{name}err' (shape: {np.shape(err)}) must be a scalar "
+                    f"or a 1D or (2, n) array-like whose shape matches "
+                    f"'{name}' (shape: {np.shape(data)})") from None
+            return data - low * ~lolims, data + high * ~uplims  # low, high
 
         if xerr is not None:
             left, right = extract_err('x', xerr, x, xlolims, xuplims)

lib/matplotlib/axes/_base.py

@@ -2312,7 +2312,8 @@ def _process_unit_info(self, datasets=None, kwargs=None, *, convert=True):
         ----------
         datasets : list
             List of (axis_name, dataset) pairs (where the axis name is defined
-            as in `._get_axis_map`.
+            as in `._get_axis_map`).  Individual datasets can also be None
+            (which gets passed through).
         kwargs : dict
             Other parameters from which unit info (i.e., the *xunits*,
             *yunits*, *zunits* (for 3D axes), *runits* and *thetaunits* (for
@@ -2359,7 +2360,8 @@ def _process_unit_info(self, datasets=None, kwargs=None, *, convert=True):
                 for dataset_axis_name, data in datasets:
                     if dataset_axis_name == axis_name and data is not None:
                         axis.update_units(data)
-        return [axis_map[axis_name].convert_units(data) if convert else data
+        return [axis_map[axis_name].convert_units(data)
+                if convert and data is not None else data
                 for axis_name, data in datasets]
 
     def in_axes(self, mouseevent):

lib/matplotlib/tests/test_units.py

@@ -166,6 +166,14 @@ def test_scatter_element0_masked():
     fig.canvas.draw()
 
 
+def test_errorbar_mixed_units():
+    x = np.arange(10)
+    y = [datetime(2020, 5, i * 2 + 1) for i in x]
+    fig, ax = plt.subplots()
+    ax.errorbar(x, y, timedelta(days=0.5))
+    fig.canvas.draw()
+
+
 @check_figures_equal(extensions=["png"])
 def test_subclass(fig_test, fig_ref):
     class subdate(datetime):